Nano Ca(OH)2 synthesis using a cost-effective and innovative method: Reactivity study

Ca(OH)2 nanoparticles in hydro-alcoholic dispersion (nanolime) are currently used for eco-compatible treatments of carbonate-based substrates in the field of Cultural Heritage conservation. Unfortunately, at present nanolime is synthesized by processes which present some drawbacks (considerable cost, multiple steps, low specific production yield), thus limiting the potential of its applications. We have developed a single-step procedure, based on an ion exchange process, making it possible to produce pure and crystalline Ca(OH)2 nanoparticles easily in water, at room temperature and ambient pressure, starting from cheap or renewable reactants. The simplicity of the process and its time- and energy-saving aspects are very promising factors for extending the production from laboratory to industrial scale. The aim of this paper is to investigate the structural and morphological features of the nanoparticles produced and to analyze the influence of crucial parameters of the synthesis process (i.e., time, water usage, reagent concentration and reaction volume) on the nanoparticles' characteristics. The nanolime produced is investigated by XRD, FTIR, TEM, and AFM techniques. The nanoparticle reactivity in the carbonation process is also investigated, by varying the suspension concentration, the solvent and relative humidity conditions. Pure, crystalline, and very reactive Ca(OH)2 nanoparticles are obtained. The nanoparticles are constituted of thin lamellas, composed of primary hexagonal nanoparticles <10 nm, irrespective of time, water employed, reagents concentration, and reaction volume.